This invention relates to channel induction furnaces such as are used for melting metals.
The channels induction furnace of the present invention finds particular application for melting aluminum. Aluminum is a metal or low density and low resistivity and therefore requires high currents to be induced in the molten metal, in comparison with other metals of higher density and higher resistivity. High current in the metal results in the generation of high forces. In a channel furnace of conventional construction, if the power input to the furnace is increased beyond a certain value, the pinch effect due to the internal forces on the metal causes a break in the continuity of metal in the loop. This causes the electric current path around the loop to be broken; the electromagnetic forces than cease and the metal will flow under gravity to re-establish the current path. Such repetitive interruptions and restorations of the electrical power are obviously undesirable. This leads to the use of a larger bath or crucible in order to give a greater head of metal to prevent the electromagnetic forces causing the metal loop to break. For this reason, with present designs of such furnaces, there are limitations to the power which can be fed into a channel furnace of given size, i.e. for heating a given quantity of metal. There are many circumstances however in which it is desirable to have a high power density inductor for a compact channel furnace having only a low head. For example, this would enable small quantities of metal to be melted more efficiently.
It is known (see for example U.K. Patent Specification No. 506980) to make the radial depth of the channel greater than the penetration depth of the alternating current at the frequency used. It is one object of the present invention still further to improve the efficiency of such a furnace.